docs: def extract_(dstore, dspath):
      """
      Extracts an HDF5 path object from the datastore, for instance
      extract(dstore, 'sitecol').
      """
      obj = dstore[dspath]
      if isinstance(obj, Dataset):
          return ArrayWrapper(obj.value, obj.attrs)
      elif isinstance(obj, Group):
          return ArrayWrapper(numpy.array(list(obj)), obj.attrs)
      else:
          return obj